Grand Canyon Monitoring and Research Center

Sediment and Geomorphology

Project Description

Erosion of sandbars (beaches) along the Colorado River in Grand Canyon was first reported in the early 1970s, approximately 10 years after completion of Glen Canyon Dam. Since then, scientific studies have been conducted to monitor changes in sandbars and changes in the amount of sand stored on the bed of the river. One of the outcomes of these studies has been the implementation of flow experiments intended to rebuild eroded sandbars, especially by the release of controlled floods, also called “high-flow experiments,” from Glen Canyon Dam. The sediment and geomorphology projects at Grand Canyon Monitoring and Research Center include the collection and processing of data to provide information needed to conduct controlled floods and to evaluate the outcome of each controlled flood and the long-term effects of controlled floods and normal dam operations on sediment-related resources.

Topographic surveys are conducted annually at a collection of long-term sandbar monitoring sites to track trends in sandbar size. The data for sandbar area and volume spanning 1990 to the most recent survey may be downloaded or plotted in an interactive web site.

Sandbars have been used as campsites by river runners and hikers since the first expeditions to the region more than 100 years ago. These campsites continue to be an important part of the recreational experience for the more than 25,000 hikers and river runners that visit the Colorado River corridor each year.

Measurements of suspended sediment transport are used to calculate the amount of sediment contributed by tributaries and the amount transported past gaging stations on the Colorado River. These data are used to calculate accumulation and evacuation of sand for each of five segments of the Colorado River in Grand Canyon and are critical in the planning and implementation of controlled floods (high-flow experiments) from Glen Canyon Dam.

The sandbars exposed along the shoreline of the Colorado River represent only a small fraction of the sand deposits in Grand Canyon, most of which are on the bed of the river in eddies and the channel. Monitoring of sediment storage tracks changes in the supply of sand available to build sandbars.

We are mapping riverbed sediments using multibeam and sidescan echo-sounders and developing automated methods to classify these sediments by grain-size using the echo strengths. These efforts result in near-continuous high-resolution maps of substrates for the purposes of habitat mapping, sediment budgeting and sediment transport modeling.

The size of the grains of sediment on the bed of the river is an important component of sediment storage monitoring. Grain size can be measured directly by collecting a sample and processing the sample in a sediment laboratory, a time-consuming and expensive process. A more efficient method is to measure grain size by capturing images of the bed. These images enable substrate classification and, in the case of sand-covered areas, bed surface grain size measurement. These data provide further understanding of sediment transport and storage processes. Collecting grain size data with an underwater digital camera allows for higher point density and faster processing times when compared to traditional bed material collection methods.

Grand Canyon Monitoring & Research Center | 2255 North Gemini Drive Flagstaff, AZ 86001 | Phone: 928.556.7380 Fax: 928.556.7100

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